Various types of inking systems have been proposed; for example, one form of inking system is used in which an ink supply roller is in continuous contact with a ductor roller see, for example, M.A.N.-Druckmaschinen-Nachrichten, issue 62, pp. 3 to 18, especially FIG. 14. Another type of construction uses intermittent ink supply, in which the ink supply roller is placed cyclically in contact with the ductor roller, see, for example, FIG. 6 of the aforementioned literature or, for example, German Pat. No. 1,093,804.
If the subject matter is to be printed on paper webs of small format, for example on sheets of lesser width than the printing machine, or on narrow strips in a rotary offset printing machine, then wetting liquid, typically water, which reaches the ink train has the tendency to spread over the entire width of the ink rollers. The wetting liquid will thus be applied over substantial regions, at the edges or lateral portions of the rollers. An excess of water will occur in the inking system which, particularly at the end regions, will lead to a water-ink emulsion with an excess proportion of water. This leads to toning, or poor printing and, additionally, the supersaturated water-ink emulsion has the tendency to splash or spray off as the rollers rotate.
Intermittently operating ductor inking systems, under normal, ordinary operating conditions, usually are not subject to this difficulty since the intermittently operating ductor can return water-ink emulsion back to the ink trough or ink well. The quantity of water-ink emulsion which is returned usually is small, however, since it is proportional to the quantity of the ink being supplied to the ink supply roller of the inking system. If then, for example, printing is to be effected on a paper substrate which is narrower than the maximum printing width of the machine, or if subject matter has to printed which requires only very little ink, then an excess water condition can also result in an intermittently operating inking system, leading to toning.
The Invention. It is an object to improve the inking system such that toning is essentially avoided, and that spraying of water-ink emulsion is substantially eliminated.
Briefly, a return roller is provided to receive water-ink emulsion which will arise or build up in the ink train, and a stripping arrangement cooperates with the return roller to strip off the emulsion building up on the return roller, and return it to the ink trough or ink well. The stripping arrangement may be in form a counter-rotating roller which may be the ductor roller itself; or in form of doctor blades, or the like.
The system thus provides for return of the water-ink emulsion which builds up on the portion of the rollers which do not have a printing function to the ink well or ink trough itself, so that occurrence of an excess water condition in the non-printing zones is effectively avoided.